1. Field of the Invention
The invention relates to process line systems and, more particularly, to the transfer of materials onto sample plates for laboratory analysis.
2. Description of the Related Art
Processing of biological materials often involves the automated transfer of sample materials onto reaction points for testing and analysis. Automated processing reduces the amount of time necessary to process large numbers of samples. For example, genetic sequencing efforts, such as the Human Genome project, involve processing of large numbers of samples, and have produced vast amounts of information for basic genetic research that have lead to advancements in health care and drug research. With these advances, scientists can move from basic genomic discoveries to associating specific phenotypes and diseases, and thereby better identify targets for drug development. Genetic sequencing involves tests of samples deposited on microarrays, in conjunction with, for example, mass spectrometry testing.
Microarrays have been used to execute tests on large batches of genetic samples to generate phenotype associations and improve interpretation of the large data sets that result from such tests. A typical microarray comprises a substrate on which a large number of reactive points are located. Testing systems typically use a one-inch square array, which is often referred to as a chip. Earlier chips have ninety-six reactive points that receive samples for testing, arranged in a grid of eight points by twelve points. More recently, chips have been produced with four times that capacity, having a 16×24 grid of 384 reactive target locations on the chip substrate. The high capacity microarrays permit the screening of large numbers of samples and can reduce reagent costs because each target location is smaller and therefore requires less reagent to be deposited for testing.
Samples are usually prepared in a sample material plate, such as a multiple-well tray called a microtiter plate (MTP). A variety of liquid reagent materials are combined in the wells and are subjected to various heating and mixing cycles. The sample preparation typically begins with empty MTPs being delivered to a processing station. The various reagents and biological materials are then added. Some of the sample processing may involve heating, cooling, and mixing of the ingredients and biological materials while in the wells of the MTP. Many high-throughput systems involve computer controlled robotic arms that pick up the MTPs, rotate, and place each MTP at the next processing station. In this way, each MTP is moved along in the sample preparation process. Some stations may take more time to complete than others, thereby creating a bottleneck that hinders increased throughput.
Typically, completed MTPs reach a processing station where the biological samples are delivered to the chip target locations, using pins that are dipped into the sample material, which loads the tip of the pin. The loaded pin is then touched to a target area on the substrate, so that the sample liquid is transferred to the target by contact deposition. Pin tools can be problematic for high throughput systems because the pins themselves may have to be changed if different sample volumes are desired, or if the nature of the liquid sample is changed.
High-throughput testing systems typically use an array of pin tools to transfer the samples onto the chip target locations. A grid of pin tools is mounted on a dispensing head, which is lowered over a multiple-well microtiter plate (MTP) at a loading station so all of the pin tools in the array are simultaneously dipped into a respective well and, when the dispensing head is withdrawn, all the pin tools are loaded with biological samples, or reagents. Thus, with one downward cycle, all the pin tools are loaded with a sample material. The dispensing head is then withdrawn from the MTP, and then lowered over a sample chip. The sample material is then transferred to the target locations on the chip by contact deposition, which is also referred to as printing.
It should be apparent that, with ninety-six (or even 384) target locations in a one-inch square area, alignment of the dispensing head with the chip is very important to the accurate delivery of samples to the target locations. Increases in the throughput of biological samples in an efficient manner requires increasing the number of pins, thereby reducing the number of load-and-print cycles, and also requires very quick alignment of the dispensing head over the chip, and also requires rapid movement from the MTP loading station to the chip.
The dispensing head with an array of pins (i.e., a block of pins) is usually aligned to a predetermined position relative to the location at which the chips will be delivered for printing. The alignment process is typically a manual process that is performed at the beginning of a processing run, such as at the beginning of a work day. Because the block is in a fixed position relative to the dispensing head, the alignment of the head to the chips should ensure that all of the pins are aligned to the target locations on a chip. Each time the processing is halted, however, a manual alignment must be performed again to ensure proper alignment and accurate placement of the pins over the chips.
A processing run may involve thousands of load-and-print dispensing head cycles. It may be necessary to halt a processing run, such as when it becomes desirable to change or replace pins or the pin block during a processing run, or when the run must be halted for a mechanical failure or to check alignment. This causes a disruption in operation because, to ensure accurate transfer, another manual alignment must be performed before proceeding with the processing run.
The alignment process after a change in pins or a changed pin block may be especially important because the new pins may be offset from the previously installed pins, relative to the dispensing head. Thus, if no check of alignment with the new pins is performed, the pin tips may make contact with the chip at different locations from before, even though the alignment of the dispensing head to the chip has not changed, or even if the dispensing head alignment has been checked and confirmed. The samples will not be accurately transferred to the target locations on the chip. Thus, changing pins or pin blocks results in not only a delay because of the alignment process, but also results in a more complicated alignment process, further slowing down the system throughput. Although current systems are capable of processing tens of thousands of samples in a day, even higher throughput systems are desired. It should be apparent that current alignment techniques cannot easily support the demands of high-throughput systems.
The wells on a MTP often contain sample materials that are themselves the result of several operations, usually involving the mixing of solutions and other processing in each of the wells, to prepare the sample materials. Therefore, the wells must have minimum dimensions to physically permit the sample preparation operations to occur. For a 384-well MTP, the wells are typically spaced apart at approximately 4.5 mm between well centers. In contrast, the target locations on a chip are typically arranged at the minimal spacing distance that can avoid sample contamination on the chip, typically at approximately 1.125 mm between target location centers, although other spacings may be used. Thus, the 384 wells on a MTP must be spaced farther apart than the 384 wells on a chip.
In a typical system, the pins of the dispensing head are arranged in the same spacing as the wells of the MTP, to permit insertion into the MTP wells and loading of the pin tips. It should be apparent that not all of the target locations on a chip can receive their samples at the same time, given the differential spacing of the pins. Therefore, systems stagger the delivery of sample material with repeated cycles of loading and printing with the pins in a dispensing head.
For example, in the spacing described above, the target locations are at a spacing that is one-fourth the spacing of the pins in a block. Therefore, for a chip having 384 target locations, a dispensing head having a 24-pin array of pins in a block must be loaded and printed through sixteen cycles of the dispensing head. It would also be necessary to perform a wash and rinse cycle of the pin block, to prevent contamination, between each loading and printing. It often can require upwards of twelve minutes to complete the loading and printing for a 384-target chip. Even a lower capacity 96-target chip would require four dispensing head cycles, which would require several minutes to complete.
Therefore, to print on all the target locations with a conventional 24-pin block, the dispensing head must load the pin block and print onto a first set of twenty-four target locations such that every fourth target location along one dimension on the chip is printed (e.g., first, fifth, ninth, and thirteenth column locations). Along the other dimension, the rows, six target locations will be printed, comprising first row, seventh, thirteenth, and so forth. The pin block must then be washed, rinsed, and loaded for the next printing cycle, during which the 24-pin block is positioned over a second group of target locations, offset or staggered from the first group, so that the second group may comprise target locations at the second, sixth, tenth, and fourteenth columns, as well as corresponding row locations.
After the second group is printed, another wash, rinse, and load cycle is repeated and then the third dispensing head cycle prints the third, seventh, eleventh, and fifteenth column of target locations, and then the fourth cycle prints the target locations for the fourth, eighth, twelfth, and sixteenth columns. In this example, the next dispensing head cycle would print in columns 17, 21, 25, and 29, followed by columns 18, 22, 26, 30, and so forth, repeating the dispensing head cycles until all wells of the 384-well chip are printed. It should be apparent that the current staggered printing operation can be a bottleneck to increasing the throughput of sample handling systems.
As noted above, samples are usually prepared in multiple-well trays called microtiter plates (MTPs). A variety of reagent materials are combined in the wells and are subjected to various heating and mixing cycles. The sample preparation typically beings with empty MTPs being delivered to a processing station. The various reagents and biological materials are then added. Some of the sample processing may involve heating, cooling, and mixing of the ingredients and biological materials while in the wells of an MTP. Many high-throughput systems involve computer controlled robotic arms that pick up the MTPs, rotate, and place each MTP at the next processing station. In this way, each MTP is moved along in the sample preparation process. Some stations may take more time to complete than others, thereby creating a bottleneck that hinders increased throughput.
Some of the reagent material may comprise a suspension of liquid and particles mixed together. It is important for the suspensions to have good mixing of liquid and particles, or solid matter, to ensure proper reactions in the MTP wells. This requirement can make working with suspension for MTP wells difficult to work with, because it may be difficult to keep the suspension adequately mixed and agitated without damaging the particles from excessive mixing and agitation. That is, suspension mixtures can be very unstable and it can be difficult to maintain them in a sufficiently suspended state.
An alternative to using a suspension mixture is to keep the particles separate from the liquid until the suspension mixture is needed. When it is necessary to mix the particles (which are typically in the form of a powder), the particles are deposited into wells of a dry particle tray, where each particle well has a predetermined volume according to the laboratory process being performed. Any excess particle material that is mounded over the top of any particle well is scraped off the top surface of the tray and into a particle reservoir. The particle tray is then quickly inverted over the microtiter plate so that the contents of each particle well fall into a corresponding well of the microtiter plate. The particle tray can be tamped with a solid object to dislodge any remaining portions of particle matter, ensuring that the proper volume of particle matter is delivered, and then the liquid and particle contents in each MTP well can be mixed to form the required suspension.
Maintaining ingredients in powder form can be advantageous, because the solid particles have greater stability and shelf life than a corresponding suspension would have, and keeping the materials in the solid state avoids the problem of keeping the suspension agitated, but the particle mixing operation described can be an excessively manual process. There is a continuing need for high-throughput biological processing systems. Such systems are becoming increasingly automated, with processing for tens of thousands of samples each working day. The manual processing associated with keeping solid particle material out of suspension until needed becomes a bottleneck to increased throughput. It should be apparent that there is a need for improved techniques for providing the suspension in MTP wells at the required time during processing of sample materials, to provide greater stability of material, reduce concerns regarding handling of suspension, and improve compatibility with increased automation systems.
Another stumbling block to increasing throughput is the requirement for some systems to perform temperature bath, referred to as thermal cycling. In a typical thermal cycling operation, an MTP plate is placed on top of a metal plate that conforms to the underside of the MTP. The temperature of the metal plate is controlled through cooling and heating cycles, as desired, thereby affecting the contents of the MTP wells. For high-throughput systems, it is important to ensure greater heat transfer rates for faster sample processing. It is also important to achieve greater uniformity of temperature cycling to ensure highly reproducible biological reactions giving clinically validated results.
Thus, there is a need for improved techniques for alignment of pins to target locations, for printing between MTP wells of one spacing to target locations at a different spacing that support higher throughput rates, for particle dispensing, and for thermal cycling operations to support increased throughput rates. The present invention fulfills this need.